Composite materials comprising a polymer matrix and granules embedded therein

ABSTRACT

The present invention provides composite materials comprising a polymer matrix comprising one or more polymers and, embedded into the polymer matrix, granules which preferably after embedding have at least one cavity which is closed off relative to the ambient environment and in which there is an underpressure relative to the standard pressure of 1 bar (100 kPa), a method for producing such composite materials, and use as insulating material.

FIELD OF THE INVENTION

The present invention is directed to composite materials comprising a polymer matrix comprising one or more polymers and, embedded into the polymer matrix, granules or shapes which preferably after embedding have at least one cavity which is closed off relative to the ambient environment and in which there is an underpressure relative to the standard pressure of 1 bar (100 kPa). The present intention also relates to a method for producing such composite materials, and to use of such composite materials as an insulating material.

BACKGROUND OF THE INVENTION

In the field of thermal insulation, vacuum insulation panels (VIPs) manufactured by enveloping a porous core material—for example, compacted fumed silica (Aerosil), fibre mats or open-cell foams—with a gas-tight sheet material and then carrying out evacuation are known. These panels permit excellent thermal insulation (thermal conductivities<3.5* 10⁻³ W*m⁻¹*K⁻¹, determined in accordance with DIN 52 612, at 10° C., are realisable), but the insulating effect suffers markedly if the gas-tight sheet is damaged. These panels, consequently, have to be produced with particular desired dimensions and installed in a protected fashion (http://www.va-q-tec.com/). Moreover, the gas-tight sheets generally have a finite barrier sealing quality, and so there is also a more or less rapid age-related deterioration in the insulating effect.

Conversely, rigid polyurethane foams have very good processing qualities. Insulating boards made of rigid polyurethane can be cut to any size, or the foam can be produced directly in the cavity that is to be filled. The latter process is commonplace in the case of refrigeration equipment (fridges). The insulating properties, however, are well below those of vacuum insulation, since minimal thermal conductivities of around 20*10⁻³ W*m⁻¹*K⁻¹ are attained (http://www.waermedaemmstoffe.com/).

The topic nexus of energy efficiency and climate protection that is presently under the spotlight has led to increased interest, not least among the manufacturers of refrigeration equipment, in innovative solutions for significant efficiency boosting—in particular by improved thermal insulation using VIPs. Solutions currently under discussion envisage the use of VIPs in combination with rigid PU foam; i.e., the panels are inserted into the cavity between inner liner and outer sheet-steel skin and then surround-foamed with polyurethane (PU). In this way, the established production process for refrigerators can be essentially retained (http://www.appliancedesign.com/Articles/Article_Rotation/BNP_GUID_(—)9-5-2006_A_(—)10000000000000893355).

In the context of the thermal insulation of buildings, the use of VIPs is substantially more problematic, since VIPs cannot be cut to size and when the gas-tight outer skin is damaged they loose their effect, yet the insulating boards are required in different sizes and shapes. In the buildings sector, moreover, the lifetime requirements are generally much higher.

SUMMARY OF THE INVENTION

The present invention provides an insulating material which combines the superlative thermal insulation of vacuum insulation panels with the establishedly multi-faceted processing possibilities of polyurethane foams.

Surprisingly it has been found that a polymer matrix into which evacuated granules or (generally) shapes have been embedded can be used as an insulating material which has both of the above mentioned properties.

The present invention accordingly provides composite materials comprising a polymer matrix comprising one or more polymers and, embedded into the polymer matrix, granules and/or shapes which have at least one cavity which is closed off relative to the ambient environment and in which there is an underpressure relative to the standard pressure of 1 bar (100 kPa).

The present invention also provides a method for producing a composite material, in which a material for producing a polymer matrix is mixed with granules and/or shapes having at least one cavity which is closed off relative to the ambient environment and in which there is an underpressure relative to the standard pressure of 1 bar (100 kPa), and from this mixture a polymer matrix is generated in which the granules are embedded.

The present invention further provides the use of the inventive composite material as an insulating material, and also articles which comprise the inventive composite material.

The composite materials of the invention have the advantage that they can be manufactured in virtually any imaginable shape and size. Moreover, the composite materials of the invention can be cut to any desired sizes and shapes without any critical loss in their good specific insulating properties. Consequently, the composite materials of the invention can be employed in a substantially more multi-faceted way than the vacuum insulation panels known from the prior art, but at the same time provide better insulation than pure PU foam insulation materials.

The composite materials of the invention also have the advantage, that they have a thermal conductivity (determined in accordance with DIN 52 612, at 10° C.) of less than 18*10⁻³ W*m⁻'*K⁻¹.

DETAILED DESCRIPTION

The composite materials of the invention, the method for their production, and the uses thereof are described by way of example below, without any intention that the invention should be confined to these exemplary embodiments. Where, below, ranges, general formulae or classes of compound are indicated, the intention is that they should encompass not only the corresponding ranges or groups of compounds that are explicitly stated, but also all sub-ranges and sub-groups of compounds which are obtainable by extraction of individual values (ranges) or compounds. Where documents are cited in the context of the present description, the intention is that their content, especially with regard to the substantive subject-matter referred to, should in its entirety form part of the disclosure content of the present invention. If average values are indicated below, the average in question, unless otherwise specified, is the numerical average. If figures in per cent are indicated below, then the percentage in question, unless otherwise specified, is % by mass.

The composite materials of the invention are distinguished by the fact that they comprise a polymer matrix comprising one or more polymers and, embedded into the polymer matrix, are granules or shapes having at least one cavity which is closed off relative to the ambient environment and in which there is an underpressure relative to the standard pressure of 1 bar (100 kPa). The underpressure is less than 500 mbar, preferably from 0.001 to 200 mbar, and more preferably from 0.1 to 100 mbar. The mass fraction of the granules in the composite material is preferably 20% to 99% by mass, and more preferably 50% to 90% by mass. The granules or shapes may consist substantially of one or more organic materials and/or of one or more inorganic materials. The expression “substantially” here is intended to denote a %-by-mass fraction of at least 70%, preferably at least 90%, based on the total mass of the granule. The granules preferably consist substantially of inorganic materials, more particularly of oxygen-containing compounds or salts of metals or semi-metals. Preferred oxygen-containing compounds are aluminium oxides or aluminosilicates or silicon dioxides or silicas, more particularly fumed or precipitated silicas. Especially preferred granules consist substantially of compacted powders of fumed silica and/or, preferably, of precipitated silica. Included in addition may be various opacifiers such as, for example, SiC, carbon black, graphite, iron oxides or TiO₂, alone or in combination, with fractions of preferably 1% to 30% by mass, more preferably 5% to 10% by mass (based on the granule or powder mass). The presence of opacifier may possibly achieve a reduction in radiative thermal conduction. Furthermore, for the purpose of mechanical stabilization, the granules or shapes may comprise fibres, such as glass, ceramic or polymer fibres, for example, and also auxiliaries from the granulation process, examples include binders.

The granules preferably have an average grain size d₅₀ of 50 μm to 100 mm, preferably from 100 μm to 50 mm and more preferably from 0.5 mm to 20 mm (determined in accordance with DIN 66165-2). In some embodiments of the present invention and in order to obtain a maximum filling level and/or for improving processing, it may be useful to use specific distributions of the grain-size distribution, such as bimodal or trimodal distributions, for example. Alternatively to granules, having a granule-grain shape and size distribution dependent on the granulating process, shapes with defined geometry, examples include spheres or cuboids, can be used. In this case, corresponding ranges as for the average grain size of the granules apply in respect of the preferred dimensions in the three directions of space.

In accordance with the present invention, the individual grains of the granule or shapes each must have at least one cavity. From a morphological view point, the cavity in question may comprise a single cavity surrounded by solid material, as in the case of a hollow sphere, for example, or may comprise a plurality of isolated closed pores, or else may comprise a network of open pores and/or channels. The granule grains or shapes preferably consist substantially of compacted powders, and so an open pore system is maintained between the individual primary particles. In some embodiments, powders which are very finely divided or even nanostructured, producing correspondingly finely structured pore systems, can be used. Preferred powders or materials used have a BET surface area of greater than 5 m²/g, more preferably of 50 m²/g to 1000 m²/g (in accordance with ISO 9277).

The granules present in the polymer matrix preferably have a porosity Φ, i.e., a ratio of the volume of the closed-off cavity to the total volume of the granule grain, of 50% to 99.9%, more preferably of 75% to 99%. The total volume of the granule or of a granule grain or shape with closed-off cavity can be ascertained by determining the displaced volume of a suitable liquid, e.g., water or ethanol. The volume of the closed-off cavities can be determined by subtracting the volume of the granule solids from the total volume. The volume of the solids can be calculated easily from the ascertained mass if the density of the solids material is known, or else the granules whose total volume has been determined are ground to an average grain size d₅₀ of 20 μm, using a mill or mortar, and the volume or density of the resultant powder is ascertained.

The cavity or cavities present in the granule grains or shapes may be closed off relative to the ambient environment by a gas-impermeable barrier composed of an appropriate material. In the case of granule grains or shapes with a closed porosity, it is generally the material of the granule grain itself that takes on this barrier function. In the case of granules or shapes with an open porosity, each individual grain, advantageously, is encapsulated by being enveloped with a suitable material, which may differ from the base material of the granule or shape. The material may be selected, for example, from plastics, metals, glasses or a combination of these substances. In some embodiments of the present invention and in order to maintain the underpressure in the cavity or pore system for as long as possible, it may be advantageous if the barrier is constructed of metal or of a glasslike compound, preferably glass, or a plastic-metal composite. With particular preference the cavities are closed off relative to the ambient environment by a barrier made of glass, more particularly silicate glass, or by a plastic-metal composite, preferably metallized plastics sheeting.

The gas atmosphere enclosed within the cavities/pores has an underpressure relative to the standard pressure of 1 bar (100 kPa). The underpressure is preferably less than 500 mbar, preferably from 0.001 to 200 mbar, more preferably from 0.1 to 100 mbar. The gas pressure can be determined by the following technique: a measured amount of granule grains having the total volume V_(granule) is destroyed in a defined, gas-tight space having the empty volume V_(test chamber). On the basis of the change in the gas pressure in this space, from P₀ before destruction of the granule grains to P_(i) after destruction of the granule grains, it is possible to determine the pressure prevailing in the pores of the granules beforehand, P_(pore), in accordance with the following equation:

P _(pore) =[P ₁(V _(test chamber) −V _(granule)(1−Φ))−P ₀(V _(test chamber) −V _(granule))]/[V _(granule)Φ]

An alternative would be to destroy the particles under water (or in another liquid which wets the particles very effectively) and to collect the gas volume released.

The composition of the gas atmosphere is arbitrary. In one embodiment of the present invention, it is preferred to use a gas atmosphere with a composition different from that of air. The gas composition is preferably set specifically and is selected so as to achieve a low thermal conductivity. There are preferably two different parameters to be observed here: firstly the gas-phase thermal conductivity of the gas composition, and secondly the free path length of the gas molecules. Preferred gases with a low gas-phase thermal conductivity are the typical propellant gases such as, for example, CO₂, hydrocarbons having 3 to 5 carbon atoms, preferably cyclo-, iso- and n-pentane, hydrofluorocarbons (saturated and unsaturated), preferably HFC 245fa, HFC 134a and HFC 365mfc, hydrofluorochlorocarbons (saturated and unsaturated), preferably HCFC 141b, oxygen-containing compounds such as methyl formate and dimethoxymethane, or hydrochlorocarbons, preferably 1,2-dichloroethane. In the case of finely structured pore systems and low gas pressures, however, the gas-phase thermal conductivity may drop below the value anticipated for the gas composition. This effect is called the Knudsen effect. The effect occurs when the free path length of the gas molecules is greater than the diameter of the pores in which the gas is located. Collisions of the gas molecules with the pore walls then become more probable than collisions of the gas molecules with one another. This may proceed to an extent such that collisions of the gas molecules with one another are suppressed entirely. Without collisions, there is no transfer of thermal energy, and gas-phase thermal conduction is switched off. In contrast to the thermal conductivity, the free path length goes up as the molar mass of the gas molecules drops. In some embodiments of the present invention, it may therefore be advantageous to use a gas with a low molar mass, such as hydrogen, helium, methane, ammonia, water or neon, for example, as insulating gas in the pores of the granule grains or shapes, if the Knudsen effect outweighs the thermal conductivity—which is actually high—of these gases.

The polymer matrix into which the granule grains or the shapes are embedded may be unfoamed or foamed. The polymer matrix is preferably a polymer foam matrix. A polymer foam matrix has the advantage that the insulating performance can be further increased relative to that of unfoamed polymers, and that, depending on the polymer material and additives employed, the foamed polymer matrix may be more flexible than an unfoamed polymer matrix of the same polymer material. Where the polymer matrix is a polymer foam matrix, this polymer foam may be of open-cell or closed-cell configuration. The polymer foam matrix is preferably a closed-cell polymer foam matrix.

The polymer matrix may comprise all known polymers, individually or in blends. The polymer matrix preferably comprises foamable polymers. Particularly preferred polymers which may be present in the polymer matrix are selected, for example, from polystyrene (PS), polyurethane (PU) and polymethyl methacrylate (PMMA). Particularly preferred polymer matrices are those which comprise rigid PUR or PIR foams. For producing a polymer foam matrix it is possible to use commonplace manufacturing methods, such as RIM (reaction injection molding) processes or extrusion processes, for example.

As already stated for the granule, the polymer matrix as well may comprise an opacifier. An opacifier may be selected, for example, from carbon black, TiO₂, graphite or SiC, and the nature and proportion of the opacifier in the polymer matrix may differ from those in the granule. The fraction of opacifier, based on the total mass of the polymer matrix, is preferably 0.5% to 30% by mass, more preferably 1% to 10% by mass.

The gas phase present in the pores of a foamed polymer matrix may differ in composition and pressure from the gas phase in the cavities and/or pores of the granule grains or shapes. The cell gas in the polymer matrix is determined substantially by the blowing agents used. Both physical and chemical blowing agents can be used in the present invention. Preferred blowing agents are those whose gas-phase thermal conductivity is lower than that of the air. Suitable physical blowing agents for the purposes of this invention are gases, for example liquefied CO₂, and volatile liquids, including, for example, hydrocarbons having 3 to 5 carbon atoms, preferably cyclo-, iso- and n-pentane, hydrofluorocarbons (saturated and unsaturated), preferably HFC 245fa, HFC 134a and HFC 365mfc, hydrofluorochlorocarbons (saturated and unsaturated), preferably HCFC 141b, oxygen-containing compounds such as methyl formate and dimethoxy methane, or hydrochlorocarbons, preferably 1,2-dichloroethane.

The composite materials of the invention can be produced in various ways. Preferred composite materials of the invention are those which are obtainable by the method of the invention, which is described below.

The method of the invention for producing a composite material of the invention is distinguished by the fact that a material for producing a polymer matrix is mixed with granules or shapes having at least one cavity which is closed off relative to the ambient environment and in which there is an underpressure relative to the standard pressure of 1 bar (100 kPa), and from this mixture a polymer matrix is generated in which the granules or shapes are embedded.

The granules or shapes that are used are produced preferably from precursors which are in powder form and have the above-described composition and properties. For this purpose it is possible to use all commonplace granulating and tableting procedures, such as fluidized-bed granulation, compacting and optionally crushing, or low-pressure extrusion, where appropriate with use of liquids for dispersing and/or of additional binders, for example. Granules and shapes obtainable in these ways frequently have an open porosity. In order to generate the underpressure that is essential to the invention within the pore system, the granules/shapes are preferably exposed to an external underpressure and/or to an elevated temperature and under these conditions are furnished with a gas-impermeable barrier layer. In the case of encapsulation at or below room temperature, the pressure (underpressure) at which the furnishing with the barrier layer takes place is preferably less than 500 mbar, more preferably from 0.001 to 200 mbar. Where elevated temperatures are employed while the barrier layer is applied, the pressure need not be lowered to such an extent, since the internal pressure reduces further on cooling of the encapsulated granules.

The barrier layer can be produced using the materials specified above for the barrier layer. The cavities are preferably closed off relative to the ambient environment by a barrier of glass. Production takes place preferably by superficial melting of the granule material or of additional additives in the marginal region of the granules. Alternatively a melt of the barrier material may be applied to the surface of the open-pored porous granules, and this melt is subsequently caused to solidify. Application may be accomplished, for example, by applying the melt to the granules by spraying or knife coating, or by immersing the granules into the melt. Solidification of the melt may be accomplished by simple cooling to room temperature.

Another method for encapsulating the granule grains is that of chemically reactive sealing, by means, for example, of silanes, or using curing polymers. For this purpose, the granule grains may be immersed into a liquid preparation of the capsule material, or the preparation may be poured over or applied by spraying to the granules, or the granules may be otherwise wetted superficially with said preparation. Alternatively to a chemically reactive encapsulation material it is also possible to use a melt of a thermoplastic polymer.

A third possible method is that of enveloping the granule grains with a gas-tight sheet. For this purpose it is preferred to use multi-ply polymeric sheets which comprise a thin metal layer as a diffusion barrier. In order to close the sheet capsules, the sheets may be adhesively bonded or welded. In some embodiments of the present disclosure, it may be advantageous to employ combinations of the aforementioned encapsulation methods in two-stage or multi-stage steps.

Encapsulation of the granules, however, is not absolutely necessary. The underpressure that is essential to the invention in the cavities of the granule grains may also be ensured by implementing the entire operation of the embedding of the granules into a polymer matrix under reduced pressure—subject to the proviso that the external polymer matrix itself forms a sufficiently gas-tight barrier, allowing the underpressure to be maintained in the granules when the composite material, after being produced, is exposed to the standard external air pressure. Another variant of this embodiment is to generate the underpressure in the cavities in the granule grains by means of chemical reactions or getter substances. Embedding may then take place at standard pressure, but the internal pressure within the cavities of the granule grains goes down after they have been embedded, as a result of chemical reactions or absorption of the gas molecules. For example, the granules may be admixed with calcium oxide, the gas phase within the cavities replaced by carbon dioxide, and the granules embedded immediately into the polymer matrix. In subsequent days, the gas pressure in the cavities goes down automatically as a result of reaction of the calcium oxide with the carbon dioxide to form calcium carbonate.

As material for producing the polymer matrix it is possible to use a polymer or a mixture of polymers, or the reactants for generating the polymer or polymers. The amount of granules/shapes and polymers to be used, and/or of their starting materials, is preferably selected such that the resultant composite material has the mass fraction of granules/shapes that was indicated above as being preferred.

In some embodiments of the present invention, it may be advantageous if the method of the invention includes at least one method step in which the material for producing the polymer matrix, or a part thereof, is at least partly in the liquid aggregate state and this liquid phase is mixed with the granules. In order to facilitate the mixing operation of polymer with granule or shapes, it may be advantageous, in some embodiments, if the polymer is converted into a liquid or fluid state by being dissolved in a suitable solvent or by melting. After the mixing operation, the polymer matrix is solidified by cooling to below the melting temperature and/or by removal of the solvent. Alternatively, the mixing operation with the granules may also take place at the stage of the starting compounds for generating the polymer matrix, i.e., with the monomers or prepolymeric compounds. In that case the polymer matrix comes about directly in the composite material as a result of a polymerization reaction or crosslinking reaction. This variant is preferred when the polymer matrix belongs to the group of the thermosets. In a further embodiment of the method of the invention, the granules or shapes are mixed with a likewise granulated polymer. Joining to form the composite material in that case takes place typically by heating, with the polymer melting or at least softening, and adhesively bonding the granules.

In some embodiments, it may be advantageous if the method of the invention includes a method step of foaming. Foaming may take place mechanically/physically or chemically. In the case of mechanical/physical foaming, air or gas, or a gas mixture, is introduced in gaseous form into a viscous polymer composition, and this viscous polymer composition is subsequently cured, causing the introduced air or gas/gas mixture to be enclosed in bubbles in the polymer composition. Polymer foams can also be generated physically by admixing a polymer composition with one or more blowing agents which, on heating, change their aggregate state from liquid or solid to gaseous and thus likewise lead to foam formation. Suitable and known blowing agents are, for example, hydrocarbons which are liquid at room temperature, such as, for example, pentanes. Where the composition of the invention includes additional blowing agents, these may be physical or chemical blowing agents. Suitable physical blowing agents for the purposes of this invention are gases, examples are liquefied CO₂, and volatile liquids, examples are hydrocarbons having 3 to 5 carbon atoms, preferably cyclo-, iso- and n-pentane, hydrofluorocarbons, preferably HFC 245fa, HFC 134a and HFC 365mfc, hydrofluorochlorocarbons, preferably HCFC 141b, oxygen-containing compounds such as methyl formate and dimethoxy methane, or hydrochlorocarbons, preferably 1,2-dichloroethane. Chemical generation of foam is possible, for example, through compounds being formed during the polymerization that are gaseous at the polymerization temperatures. One typical chemical blowing agent is, for example, water, which is formed in polymerization reactions that are based on a condensation reaction. Besides water, other chemical blowing agents may also be used. In the case of the production of polyurethane foams, for example, those which react with the isocyanates used and in so doing give off gas, such as water or formic acid.

Using the example of a composite material with a foamed polyurethane matrix, various versions of the method of the invention will be discussed in more detail. Foamed polyurethane is generally a highly crosslinked thermoset which is neither soluble in common solvents such as water, ethanol or acetone, nor is meltable (without decomposition). Mixing with the granules therefore takes place preferably at the stage of monomeric and/or prepolymeric compounds. A polyurethane system for the production of insulating foams generally features two components (A) and (B), with one component composed of compounds having reactive hydrogen atoms, known as the polyol component (A), and the second component (B) having one or more isocyanates. Customary auxiliaries and adjuvants may be formulated into the polyol component (A) or metered in separately. The granules or shapes are mixed preferably with the polyol component, with the isocyanate component or—with particular preference—with a fresh reaction mixture of these components. The two first-mentioned cases are suitable only for low levels of filling and small grain diameters on the part of the granules, since the granules and shapes must be pre-dispersed in component (A) or (B), and this dispersion must then be intimately mixed with the second component. The preferred case of incorporation of the granules/shapes into a fresh reaction mixture of (A) component and (B) component allows the trouble-free processing of large grain diameters. The incorporation of granules/shapes in the reaction mixture may take place prior to transfer to the mold, or else granules/shapes are introduced as packing or filling in a hollow mold and are infiltrated, or the grains surround-foamed, with the liquid, foaming reaction mixture. For the production of insulating boards, a continuous method analogous to the production of polyurethane insulating boards, by the double transport belt method, is also conceivable. In that case the granules/shapes can be scattered onto the lower top layer either before or after the application of the polyurethane reaction mixture, with the individual grains being surround-foamed. In this case the composite material is cured by the polyaddition reaction involving crosslinking to form the polyurethane.

The typical composition of a polyurethane system is described in more detail below:

As polyol components (A) it is possible to use the compounds customary for the formulation of insulating foams, examples are polyether polyols and polyester polyols. Polyether polyols can be obtained by reacting polyhydric alcohols or amines with alkylene oxides. Polyester polyols are based preferably on esters of polybasic carboxylic acids (usually phthalic acid or terephthalic acid) with polyhydric alcohols (usually glycols).

As (poly)isocyanate component (B) it is possible to use the compounds customary for the formulation of insulating foams, examples are 4,4′-diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HMDI) and isophorone diisocyanate (IPDI). Particularly suitable is the mixture of MDI and its analogues with higher degrees of condensation, having an average functionality of 2 to 4, this mixture being known as “polymeric MDT” (“crude MDI”).

A suitable ratio of isocyanate and polyol, expressed as the index of the formulation, is situated in the 50-500 range, preferably 100-350. The index describes the ratio of isocyanate actually used to isocyanate calculated (for a stoichiometric reaction with polyol). An index of 100 stands for a molar ratio of the reactive groups of 1:1.

As auxiliaries and additives it is possible to use the compounds customary for the formulation of insulating foams, including catalysts, cell stabilizers, blowing agents, flame retardants, fillers, dyes and light stabilizers.

Suitable catalysts for the purposes of this invention are, for example, substances which catalyze the gel reaction (isocyanate-polyol), the blowing reaction (isocyanate-water) or the dimerization or trimerization of the isocyanate. Typical examples are the amines triethylamine, dimethylcyclohexylamine, tetramethylethylenediamine, tetramethylhexanediamine, pentamethyldiethylenetriamine, pentamethyldipropylenetriamine, triethylenediamine, dimethylpiperazine, 1,2-dimethylimidazole, N-ethylmorpholine, tris(dimethylaminopropyl)hexahydro-1,3,5-triazine, dimethylamino-ethanol, dimethylaminoethoxyethanol and bis(dimethylaminoethyl) ether, tin compounds such as dibutyltin dilaurate and potassium salts such as potassium acetate and potassium 2-ethylhexanoate. Suitable amounts for use are guided by the type of catalyst and are situated typically in the range from 0.05 to 5 parts by weight, or 0.1 to 10 parts by weight for potassium salts, based on 100 parts by weight of polyol.

Suitable cell stabilizers are, for example, surface-active substances such as, for example, organic surfactants or, preferably, silicone surfactants (polyetherpolydimethylsiloxane copolymers). Typical amounts of polyethersiloxane cell stabilizers for use are 0.5 to 5 parts by weight per 100 parts by weight of polyol, preferably 1 to 3 parts by weight per 100 parts by weight of polyol.

The foamable formulation may be admixed with water as a chemical blowing agent, since it reacts with isocyanates and gives off carbon dioxide gas in the process. Suitable amounts of water for the purposes of this invention are dependent on whether, in addition to the water, physical blowing agents are used as well, or not. In the case of purely water-blown foaming, the levels for the water content are preferably 1 to 20 parts by weight per 100 parts by weight of polyol; where other blowing agents are used in addition, or where foaming takes place under reduced pressure, the amount for use reduces preferably to from 0.1 to 5 parts by weight of water per 100 parts by weight of polyol. Suitable physical blowing agents have already been specified.

Insulating foams for the heat insulation of buildings are subject to fire control requirements and must preferably be made flame retardant. In principle all customary flame retardants are suitable. Used with preference as flame retardants are preferably liquid organic phosphorus compounds, such as halogen-free organic phosphates, e.g., triethyl phosphate (TEP), halogenated phosphates, e.g., tris(1-chloro-2-propyl)phosphate (TCPP) and tris(2-chloroethyl)phosphate (TCEP), or organic phosphonates, e.g., dimethyl methanephosphonate (DMMP), dimethyl propanephosphonate (DMPP) or solids such as ammonium polyphosphate (APP) or red phosphorus. Additionally suitable as flame retardants are halogenated compounds, examples are halogenated polyols, and also solids such as expandable graphite and melamine.

A typical polyurethane or polyisocyanurate insulating foam formulation in the sense of this invention would result in a density of 5 to 50 kg/m³ and have the following composition:

Component Weight fraction Polyol 100 (Amine) catalyst 0.05 to 5    Potassium trimerization catalyst 0 to 10 Polyethersiloxane 0.5 to 5   Water 0.1 to 20   Blowing agent 0 to 40 Flame retardant 0 to 50 Isocyanate index: 50-500

The formulations of the invention can be processed to rigid foams by any of the methods familiar to the skilled person, as for example in a manual mixing procedure or, preferably, using high-pressure foaming machinery.

As an alternative to the surround-foaming of encapsulated granules, it is also possible to use uncapsulated granules, in which case the entire surround-foaming operation takes place with a closed-cell rigid foam under reduced pressure. For this purpose the granules are placed in a hollow mold with a gas-tight closure, there being connected to this mold a vacuum pump and the mixing head of a high-pressure foaming machine. When the hollow mold has been evacuated to the desired pressure, the foaming machine is used to inject the liquid polyurethane reaction mixture into the mold. The reaction mixture runs into the cavities between the granule grains and begins to foam, and the expanded foam envelopes the granule grains. After the polyurethane foam has cured, the result is a composite material in which there is an underpressure not only in the cavities in the granules but also in the foam cells. The mechanical strength of the foam ought therefore to be sufficiently high to withstand the pressure difference (between internal pressure and the external air pressure) without signs of shrinking. For this purpose, generally speaking, the required foam density will be higher than is usual for polyurethane insulating foams. The pressure for the surround-foaming of the granules is preferably less than 200 mbar, more preferably less than 100 mbar—the pressure difference relative to the standard pressure, therefore, is at least 0.8 bar and more preferably 0.9 bar or more.

Additionally necessary is the adaptation of blowing agent type and amount to the underpressure foaming. As well as this batch mold foaming, continuous production methods of insulating boards in a double belt process, or of freely risen slab stock foams are imaginable, with the entire production line encased with an underpressure chamber. The construction of such a line may be guided by the “VPF process” that is customary in the production of flexible foams under reduced pressure.

As a further example, the production of a composite material with a foamed polystyrene matrix will be discussed in more detail. In this case, the preferred starting material for the polymer matrix comprises granules, preferably encapsulated granules, of polystyrene with incorporated blowing agent. These expandable polystyrene granules are mixed with the granules or shapes to be embedded. As a result of subsequent heating of the granule mixture, preferably in a hollow mold having the desired geometry, the polystyrene expands to form a foam and at the same time bonds adhesively to itself and to the embedded granules, to form a coherent molding.

The amount of granules to be used and of polymer and/or starting materials thereof to be used is preferably selected such that the resulting composite material has the mass of granules indicated above and/or has the mass ratio indicated above.

The composite material of the invention may be used in particular as insulating material. This insulating material is preferably used for the insulating of buildings, of space, air, open-water and/or land vehicles or of parts of cooling or heating systems and assemblies. The composite materials of the invention can be used as insulating material in refrigeration equipment and hot-water reservoirs, and have the advantage in these cases that they can be produced directly in the cavity to be filled. The same applies to the filling of profiles for construction purposes, examples are window frames or door frames, roller shutter elements, sectional gates, etc. Furthermore, the composite materials of the invention can be used for insulating pipelines (e.g., local and district heating lines).

A distinctive feature of corresponding articles of the invention is that they comprise a composite material of the invention.

In the examples given below, the present invention is described on an exemplary basis, without any intention that the invention—the scope of which is evident from the overall description and the claims—should be restricted to the embodiments specified in the examples.

EXAMPLES Example 1 Production of Granules

80% by weight of AEROSIL200 (fumed silica from Evonik Industries AG, BET surface area 200 m²/g), 15% by weight of AROSPERSE 15 (thermal carbon black from Orion Engineered Carbons) and 5% by weight of glass fibres (glass fibre slithers, approximately 12 mm fibre length) were intimately mixed. This mixture was transferred in 0.6 g portions into a cylindrical compression mold with a diameter of 2 cm and compressed by means of a hydraulic press to form tablets each with a height of 1 cm. The density of the tablets was approximately 200 kg/m³.

Example 2 Encapsulation of Evacuated Granules

The tablets produced in Example 1 were enveloped with a metallized sheet (multi-layer laminate from TOYO with PET outer layer, aluminium barrier layer and PE internal layer) by being placed between two plies of this sheet, followed by the two plies being welded thermally to one another in an annular fashion around the tablets. Within the annular weld seam, a small gap remained open, to which an oil-sealed rotary slide vacuum pump was attached via a tube. With the aid of the vacuum pump, the tablet was evacuated for 10 minutes and then under vacuum the opening in the film was welded, thus closing off the tablet in a gas-tight fashion. The protruding margin of the film was cut off up to the weld seam.

Example 3 Production of a Composite Material From Encapsulated Granules and Foamed Polyurethane Matrix

The polymer matrix used was a rigid polyurethane foam formulation in accordance with Table 1.

TABLE 1 PUR formulation Component Weight fraction Daltolac R 471*   100 parts N,N-Dimethylcyclohexylamine  1.5 parts Water  2.6 parts Cyclopentane  13.1 parts TEGOSTAB ® B 8462**  1.5 parts Desmodur 44V20L*** 198.5 Parts *Polyether polyol from Huntsman **Foam stabilizer from Evonik Industries AG ***Polymeric MDI from Bayer, 200 mPa * s, 31.5% by weight NCO, functionality 2.7

The polyurethane foaming operations were conducted in a manual mixing procedure. Polyol, amine catalyst, water, foam stabilizer and blowing agent were weighed out into a beaker and mixed with a plate stirrer (6 cm diameter) at 1000 rpm for 30 seconds. Re-weighing was used to determine the amount of blowing agent evaporated during the mixing operation, and this amount was added again. Then the MDI was added and the reaction mixture was stirred at 3000 rpm with the stirrer described for 5 seconds, then immediately transferred to an aluminium mould thermostated at 45° C. and measuring 50 cm×25 cm×5 cm, lined with polyethylene film. The amount of foam formulation used here was 15% above the amount necessary to at least fill the mold. After 10 minutes, the foam board was demolded. Using a band saw, a slice measuring 50 cm×25 cm×0.5 cm was sawn from this board. This slice was placed on the base of the aluminium mold, which was again lined with polyethylene film, and the tablets, produced as described above and encapsulated under vacuum, were laid out on top of the slice in three layers, each disposed tightly against one another. In the same way as for the first foaming operation, polyurethane reaction mixture was again prepared by stirring, then poured over the tablets with the mold lid opened, and the lid was immediately closed. After a further 10 minutes' curing time, the completed composite material was demolded.

The resultant board of the composite material was cut with a band saw to a size of 20 cm×20 cm×5 cm, and the thermal conductivity of this specimen was measured using a Hesto HLC-A90 thermal conductivity meter. The measurement value was 15.8*10⁻³ W*m⁻¹*K⁻¹. This value is well below that of rigid polyurethane foam. For comparison, a rigid polyurethane foam board produced with the same formula but without embedded granules was measured. Its thermal conductivity was 22.5*10⁻³W*m⁻¹*K⁻¹.

Example 4 Production of a Composite Material by Enveloping Unencapsulated Granules With Rigid Polyurethane Foam at Underpressure

The polymer matrix used was a rigid polyurethane foam formulation in accordance with Table 2.

TABLE 2 PUR formulation 2 Component Weight fraction Daltolac R 471*   100 parts N,N-Dimethylaminoethoxyethanol  0.5 parts Triethylenediamine, 33% in  0.5 parts dipropylene glycol Water  0.5 parts TEGOSTAB ® B 8462**  2.0 parts Desmodur 44V20L*** 189.2 parts *Polyether polyol from Huntsman **Foam stabilizer from Evonik ***Polymeric MDI from Bayer, 200 mPa * s, 31.5% by weight NCO, functionality 2.7

The polyurethane foaming procedures were carried out using a KraussMaffei RIM-Star MiniDos high-pressure foaming machine with MK12/18ULP-2KVV-G-80-I mixing head. Polyol, catalysts, water and foam stabilizer were weighed out, mixed thoroughly and transferred as a mixture into the working container of the machine. The raw materials—polyol mixture and isocyanate—were heated at 35° C., the pressures were 130 bar for the polyol and 140 bar for the isocyanate, and the total discharge rate was 200 g/s. An aluminium mold thermostated at 45° C. and measuring 50 cm×25 cm×5 cm, also fitted with a gas-tightly closing lid with a central pouring hole and a side connection for a vacuum pump (protected from foam penetration by a screen), was lined with polyethylene film and sealed, the mixing head was placed into the pouring hole in a gas-tight fashion, and the hollow mold was evacuated to 200 mbar using a membrane vacuum pump with vacuum controller. Polyurethane reaction mixture was injected into the mold by means of the foaming system, the amount of this reaction mixture being 15% above the amount necessary to at least fill the mold. After 10 minutes, the foam board was demolded. A band saw was used to saw two slices measuring 50 cm×25 cm×0.5 cm from this board. One slice was placed on the base of the aluminium mold, which was lined with polyethylene film again, and the unencapsulated tablets produced as described above were laid out on top of the slice in three layers, each arranged closely against one another. The second slice was attached to the mold lid using double-sided adhesive tape, and the pouring hole was cut out. The mold was sealed, evacuated for 10 minutes each in 3 cycles and ventilated with carbon dioxide. After that it was evacuated to 200 mbar again and after 10 minutes, in the same way as for the first foaming operation, polyurethane reaction mixture was injected. After a further 10 minutes' curing time, the completed composite material was demolded.

The resultant board of the composite material was cut with a band saw to a size of 20 cm×20 cm×5 cm, and the thermal conductivity of this specimen was measured using a Hesto HLC-A90 thermal conductivity meter. The measurement value was 17.9*10⁻³W*m⁻¹*K⁻¹.

While the present disclosure has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in forms and details may be made without departing from the spirit and scope of the present disclosure. It is therefore intended that the present disclosure not be limited to the exact forms and details described and illustrated, but fall within the scope of the appended claims. 

What is claimed is:
 1. A composite material comprising a polymer matrix comprising one or more polymers and, embedded into the polymer matrix, granules which have at least one cavity which is closed off relative to an ambient environment and in which there is an underpressure relative to a standard pressure of 1 bar (100 kPa).
 2. The composite material according to claim 1, wherein the underpressure is less than 500 mbar.
 3. The composite material according to claim 1, wherein the at least one cavity is closed off relative to the ambient environment by a bather composed of a glasslike compound or of a plastic-metal composite.
 4. The composite material according to claim 1, wherein the polymer matrix is a closed-cell polymer foam matrix.
 5. The composite material according to claim 4, wherein the polymer foam matrix is a rigid polyurethane or polyisocyanurate foam.
 6. The composite material according to claim 1, wherein the granules comprise a material having a BET surface area of greater than 5 m²/g,.
 7. The composite material according to claim 1, wherein the granules consist substantially of compacted powders of fumed silica or precipitated silica.
 8. A method for producing a composite material comprising mixing a material for producing a polymer matrix with granules having at least one cavity which is closed off relative to an ambient environment and in which there is an underpressure relative to a standard pressure of 1 bar (100 kPa), and embedding the granules within the polymer matrix.
 9. The method according to claim 8, wherein said embedding the granules comprises subjecting open-pored porous granules to an underpressure and furnishing the open-pored porous granules with an air- or gas-impermeable barrier layer.
 10. A method for producing a composite material comprising subjecting unencapsulated, open-porously porous granules to an underpressure; and embedding said granules into a polymer matrix, wherein the embedding comprises enveloping the granules with said polymer matrix, while maintaining said underpressure in cavities of the granules.
 11. The method according to claim 10, wherein the polymer matrix is a polymer or a mixture of polymers or are the reactants for generating the polymer or polymers.
 12. The method according to claim 10, wherein the polymer matrix is a polymer or a mixture of polymers or are the reactants for generating the polymer or polymers.
 13. The method according to claim 8, further comprising foaming.
 14. The method according to claim 10, further comprising foaming.
 15. An insulating material comprising a composite material according to claim
 1. 16. The insulating material according to claim 15, wherein said insulating material is used for insulating buildings, including windows, doors and roller-shutter boxes, for insulating space, air, open-water and/or land vehicles, for insulating pipelines, or for insulating parts of cooling or heating units or assemblies, refrigeration equipment, hot-water/coolant reservoirs, swimming-pool covers and swimming-pool insulation systems.
 17. An article comprising a composite material according to claim
 1. 